The present invention relates to a hollow shrinkable fiber that has good shrinkability as well as being excellent in terms of bulkiness, a lightweight feeling and warmth retention, and is suitable for manufacturing pile products.
In general, hollow fibers have various special features such as having body, being bulky with low apparent density, and having good warmth retention and water absorption properties. The use of hollow fibers in pile products has thus frequently been experimented with. A common pile product is a stepped pile comprising guard hairs and down hairs. A method commonly adopted for manufacturing such a stepped pile is to use non-shrinkable fibers as the guard hair fibers and shrinkable fibers as the down hair fibers, and to carry out heat treatment during the pile processing so that the shrinkable fibers are shrunk and a height difference is produced between the guard hairs comprising the non-shrinkable fibers and the down hairs comprising the shrinkable fibers. Relatively thick fibers are used as the guard hair fibers, and moreover this part of the pile is not required to be shrinkable, and hence there are many cases of hollow fibers being used as the guard hair fibers. However, in a pile product, the number of guard hairs is generally lower than the number of down hairs, and hence the overall bulkiness of the pile product tends to be determined mainly by the bulkiness of the part in which the down hairs are closely gathered. The desired texture, bulkiness and lightweight feeling of a pile product therefore cannot be realized merely by using hollow fibers as the guard hairs. There are thus calls for hollow fibers that are sufficiently thin and shrinkable as to be usable as down hairs. However, the fineness of the fibers used as the down hairs in pile products is 10 dtex or less, generally 2 to 7 dtex, and conventionally it has been difficult to manufacture hollow fibers that are both that thin and satisfy the other properties required of down hair fibers. For example, in the past many acrylic fibers having a single hollow structure, i.e. a single void in the fiber cross section, have been proposed. However, there has been a problem in that, if one attempts to obtain a sufficient void ratio with such a single hollow structure, then the fiber becomes weak due to the reduction in the thickness of the skin part (also called the shell part), which is the outer peripheral part in the fiber cross section, and hence under external pressure the fiber is squashed and does not recover, resulting in it being impossible to achieve the original functions of the hollow fibers, namely bulkiness and a lightweight feeling. To resolve this problem, in Japanese Patent Application Laid-open No. H7-90721, a method is proposed in which a plurality of substantially independent void parts are formed with a uniform spacing therebetween in the fiber cross section, thus obtaining a high void ratio. However, in this method, a modified sheath-core conjugate nozzle is used, leading to problems of industrial productivity being poor and the manufacturing cost being high. Moreover, methods of manufacturing hollow fibers by adding a blowing agent have been disclosed in Japanese Patent Application Laid-open No. S58-149313 and Japanese Patent Application Laid-open No. S62-78210. However, with these methods, there are problems in that there is unevenness in the position of formation and shape of the hollow portion, leading to a drop in colorability and inadequate realization of functions of the hollow fibers such as bulkiness and a lightweight feeling.
An object of the present invention is to resolve the above problems, and to provide a hollow shrinkable fiber for pile having a hollow form similar to that of natural fur, capable of recovering easily after the hollow portion thereof has been squashed under external pressure, having properties such as bulkiness, a lightweight feeling and warmth retention not achievable conventionally, and capable of being used as down hairs in a pile product, along with a method of manufacturing this hollow shrinkable fiber, and a pile product manufactured using the hollow shrinkable fiber.
A hollow shrinkable fiber for pile according to the present invention comprises a synthetic fiber, has a marrow-like or network-like hollow portion comprising a large number of voids in a core part in the fiber cross section, has a void ratio in the fiber cross section of 10 to 50%, and has a dry heat shrinkage percentage of at least 15%. The synthetic fiber preferably comprises a polymer containing a copolymer of acrylonitrile and a halogen-containing vinyl monomer.
Moreover, a method of manufacturing a hollow shrinkable fiber for pile according to the present invention is characterized by carrying out wet spinning of a copolymer of acrylonitrile and a halogen-containing vinyl monomer, and subjecting the wet fiber thus obtained to steam treatment and drying treatment, and then to heat treatment to form a hollow portion in the fiber. It is preferable for the solvent content of the fiber to be reduced to 5 wt % or less through the steam treatment, for the liquid content of the fiber to be made to be 5 to 50 wt % through the drying treatment, and for drawing treatment to be carried out after the heat treatment. Moreover, it is preferable for the heat treatment to be carried out at a temperature in the range 120 to 180xc2x0 C., and for the fiber to be elongated by a factor of 1.1 to 2.3 at a temperature in the range 90 to 150xc2x0 C. during the drawing treatment. Moreover, when the fiber obtained through the above-mentioned method is crimped, it is preferable to carry out the crimping by heating to a temperature 1 to 10xc2x0 C. below the glass transition temperature of the fiber.
The hollow shrinkable fiber for pile of the present invention as described above is suitable for use as the down hairs of a pile product.
Following is a more detailed description of the present invention. The hollow shrinkable fiber of the present invention comprises a synthetic fiber. There are no particular limitations on this synthetic fiber, with examples including an acrylic fiber, a polyamide fiber, a polyester fiber, a polyolefin fiber, a vinyl chloride fiber, a vinylidene chloride fiber and a polyvinyl alcohol fiber. However, from the viewpoint of the product quality and texture of a pile product suitable for use as artificial fur or in stuffed toys or the like, an acrylic fiber is particularly preferable. As such an acrylic fiber, one comprising a copolymer of 30 to 80 wt % of acrylonitrile and 20 to 70 wt % of a monomer copolymerizable with acrylonitrile is preferable. Examples of such a monomer copolymerizable with acrylonitrile include, for example, acrylic acid, methacrylic acid, vinyl chloride, vinylidene chloride, vinyl esters such as vinyl acetate, vinylpyrrolidone, vinylpyridine and alkyl-substituted derivatives thereof, acrylic acid esters, methacrylic acid esters, acrylic acid amides, methacrylic acid amides and monoalkyl- or dialkyl-substituted derivatives thereof, and styrenesulfonic acid, methallylsulfonic acid and metal salts and amine salts thereof. Out of these monomers, to make the fiber fire-resistant, it is preferable to use a halogen-containing vinyl monomer. Vinyl chloride or vinylidene chloride is preferable as this halogen-containing vinyl monomer.
When it is said that there is a hollow portion in the fiber cross section in the present invention, what is meant is that there are one or more voids. In fact, the fiber of the present invention has, as the hollow portion, a marrow-like or network-like hollow portion comprising a large number of voids in a core part of the fiber cross section. This fiber cross section having a marrow-like or network-like hollow portion in the core part thereof is similar to the cross section of a hair in the natural fur of an animal such as a mink or a sable. What is meant by such a fiber cross section is that a large number of voids of different shapes are formed irregularly as in bone marrow or a network in the core part, which is in the center of the fiber cross section (as opposed to the compact skin part, which is at the periphery of the fiber cross section). Examples are shown in FIGS. 1 and 2, wherein the black parts are the voids. The definition of the hollow portion in the fiber cross section in the present invention thus does not include a single (total) hollow, or a hollow portion comprising a large number of voids arranged regularly with a uniform spacing therebetween, as produced, for example, through sheath-core composite spinning.
Moreover, the void ratio of the fiber cross section in the present invention means the proportion of the total area of the fiber cross section (the area of the portion A plus the area of the portion B in the schematic view of the fiber cross section shown in FIG. 3) that is taken up by the area of the marrow-like or network-like hollow portion comprising the large number of irregularly shaped voids (the area of the portion B in FIG. 3, i.e. the total area of the large number of voids that make up the hollow portion). In the fiber of the present invention, it is preferable for this void ratio to be in the range 10 to 50%. If the void ratio is less than 10%, then the inherent properties of a hollow fiber, namely bulkiness and a lightweight feeling, will be poor. If the void ratio is greater than 50%, on the other hand, then the skin part will be thin and the fiber will be weak to external pressure, leading to rupture, and hence again to the bulkiness and lightweight feeling being poor. To give an acrylic fiber a sufficient lightweight feeling, it is thus preferable for the void ratio to be in the range 20 to 40%.
Moreover, the fiber of the present invention is a shrinkable fiber having a dry heat shrinkage percentage of at least 15%. In the present invention, the dry heat shrinkage percentage is the shrinkage percentage determined from the length of the fiber before shrinkage and the length of the fiber after shrinking by carrying out heat treatment for 20 minutes at a temperature of 100 to 150xc2x0 C. in a convection oven type dryer. It is undesirable for the dry heat shrinkage percentage of the fiber to be less than 15%, since in this case, when the fiber is used as a down hair fiber in a pile product, the height difference effect obtained though the difference in shrinkage between the guard hair fibers and the down hair fibers will tend not to be sufficiently obtained. Moreover, although there is no limitation on the maximum value of the dry heat shrinkage percentage of the fiber, this maximum value will be about the same as ordinary shrinkable fibers, namely about 30%. The dry heat shrinkage percentage of the hollow shrinkable fiber of the present invention is thus generally in the range 15 to 35%.
To manufacture the hollow shrinkable fiber of the present invention, an acrylic copolymer as described above is dissolved in an organic solvent such as acetone, acetonitrile, dimethylformamide or dimethylsulfoxide, or an inorganic solvent such as zinc chloride, nitric acid or thiocyanogen, to produce a spinning stock solution, and then wet spinning is carried out using this spinning stock solution. So long as there is no impediment to the spinning, additives such as inorganic or organic pigments or stabilizers that improve corrosion prevention, coloration prevention, light fastness or the like may be added to the spinning stock solution. The wet fiber obtained from the wet spinning is next subjected to steam treatment so as to reduce the solvent content to preferably no more than 5 wt %, more preferably no more than 3 wt %. Solvent is removed from the fiber through this steam treatment, and hence the fiber, which was in a wet state, gradually coagulates, resulting in a relatively compact skin part forming at the periphery of the fiber cross section, and moreover a relatively coarse core part forming in the center of the fiber cross section. The steam treatment is preferably carried out using saturated water vapor. Next, the fiber is dried to adjust the liquid contentxe2x80x94which includes both the solvent and waterxe2x80x94to be in a prescribed range, and make the fiber more compact. Even though this drying treatment is carried out, because solvent was removed through the steam treatment, the inside of the fiber is not prone to becoming completely compact, but rather remains in a state in which a hollow portion can be formed easily during subsequent processing. Nevertheless, if the fiber were made completely compact right through to the inside through harsh drying treatment, then it would not be possible to form a hollow portion inside the fiber through the subsequent heat treatment. It is thus preferable to carry out the drying treatment under gentle conditions. Specifically, the extent of the drying treatment should be such as to remove moisture from the fiber which has become moist through the steam treatment after the wet spinning, and also to eliminate through heat fusion microvoids that have appeared in the relatively compact skin part. The drying treatment can be carried out using publicly known equipment, but the temperature and time are set such that, through the drying treatment, the liquid (water plus solvent) content of the fiber becomes preferably 5 to 50 wt %, more preferably 10 to 30 wt %. By adjusting the liquid content of the fiber to be in such a range, a compact skin part and a coarse core part are formed. Next, the fiber having the compact skin part and the coarse core part is subjected to heat treatment at a temperature higher than that of the above drying treatment, thus forming a marrow-like or network-like hollow portion comprising a large number of voids in the core part in the center of the fiber cross section. Specifically, because the skin part of the fiber has a compact structure, a regular fiber structure is formed in the axial (length) direction of the fiber through the heat treatment, resulting in a strong continuous structure. The coarse core part in the center of the fiber cross section, on the other hand, remains coarse, and it is thought that shrinkage occurs at random through shrinkage stress and the like due to the heat, resulting in formation of irregular voids of different shapes in the core part, i.e. in the formation of a hollow portion. The heat treatment may be carried out through normal dry heat treatment or wet heat treatment using a hot air current or the like, or in a constant temperature bath using an organic compound such as polyethylene glycol or glycerine; one such method may be used, or two or more methods may be used in combination. The heat treatment is preferably carried out at 120 to 180xc2x0 C. By carrying out heat treatment under such conditions, a hollow portion is formed and a fiber having a void ratio of 10 to 50% can be obtained. For example, in the case of an acrylic fiber, it is undesirable for the heat treatment to be carried out at above 180xc2x0 C., since excessive shrinkage will then be prone to occur. Moreover, if the heat treatment is carried out at below 120xc2x0 C., then there will be insufficient heat conduction, and hence it will not be possible to obtain a high void ratio. For such reasons, it is yet more preferable to carry out the heat treatment at a temperature in the range 140 to 160xc2x0 C. During the heat treatment, 5 to 15% relaxation may also be carried out.
Furthermore, to make the dry heat shrinkage percentage of the fiber at least 15%, it is necessary to carry out drawing treatment. For example, in the case of an acrylic fiber, a shrinkage percentage of at least 15% can be obtained by drawing by a factor of 1.1 to 2.3 at a drawing temperature of 90 to 15xc2x0 C. If the drawing temperature is less than 90xc2x0 C., then heat conduction will be insufficient, and it will be difficult to draw to the prescribed draw magnification. If, on the other hand, the drawing temperature is greater than 150xc2x0 C., then a high shrinkage percentage will be obtained, but it will be necessary to heat to a high temperature when shrinking the fiber during pile processing or the like, and hence such a high drawing temperature is undesirable. For such reasons, it is yet more preferable for the drawing temperature to be in the range 105 to 135xc2x0 C.
Note that, with objects such as improving the ease of carrying out shrinkage processing during pile manufacture and improving the texture of the pile product, it is possible to apply a silicone oil or the like onto the fiber, so long as there is no impediment of the objects of the present invention. The oil application may be carried out either before or after the drying treatment.
Furthermore, to manufacture a pile product through sliver knitting using a fiber obtained as described above, it is necessary for producing the sliver to crimp the fiber. In this case, the fiber is preferably crimped by heating to a temperature 1 to 10xc2x0 C. below the glass transition temperature of the synthetic resin that makes up the fiber. The reason for this is that, if crimping is carried out at a temperature equal to or above the glass transition temperature, then thermal setting of the fiber structure will occur during the crimping, and hence the fiber will become fixed in a state in which the hollow portion is squashed and unable to recover, whereas if the heating temperature during the crimping is too low, then, although the hollow portion will be able to recover after being squashed, rupture will occur during hollow portion formation in some of the fibers, and hence it will not be possible to obtain a sufficient feeling of volume; moreover, if the heating temperature during the crimping is 20xc2x0 C. or more below the glass transition temperature, then crimp formation will be poor, and it will not be possible to produce the sliver.
An example of a method of obtaining a pile product from the hollow shrinkable fiber of the present invention is to cut the crimped hollow shrinkable fiber to a prescribed fiber length, blend such cut crimped hollow shrinkable fibers with non-shrinkable fibers that have been crimped with a shrinkage percentage of not more than 10% and have a fiber length at least 10 mm longer than that of the hollow shrinkable fibers to make a sliver, then carry out knitting using a high pile knitting machine, next coat the rear face of the pile thus obtained with an acrylic acid ester adhesive and carry out drying treatment for 3 to 10 minutes in a temperature range of 120 to 150xc2x0 C. to shrink the hollow shrinkable fibers, and then carry out a combination of high/medium/low temperature polishing and shirring to finish to a high pile.
In such a pile product, it is preferable for the hollow shrinkable fiber of the present invention to be used as the down hairs as described above. As the guard hairs, on the other hand, it is preferable to use a non-shrinkable fiber; a normal non-shrinkable fiber may be used, but a publicly known non-shrinkable hollow fiber is more preferable. Moreover, it is also possible to manufacture a pile product using the hollow shrinkable fiber of the present invention for the whole pile product, thus obtaining a pile product having an excellent feeling of volume.